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EU legislation related to Waste Incineration

The waste incineration sector has been the subject of extensive legislative requirements at regional, national and European level for many years.

In addition to the requirements of the IPPC Directive, the incineration (and associated) sector is also subject to the requirements of specific legislation. At present, the following EU-directives are in force for waste incineration plants:

  • Waste Incineration Directive 2000/76/EC for the incineration of waste (including co-incineration).

This directive sets the minimum requirements in respect of permissible emissions, monitoring and certain operational conditions. The scope of 2000/76/EC is broad (certain exclusions are specifically listed in Article 2) and does not have a lower capacity limit.

The Directive 2007/76/EC on the incineration of waste covers incineration and co-incineration with a view on prevention or limiting negative effects on the environment. In order to guarantee complete waste combustion, the Directive requires all plants to keep the incineration or co-incineration gases at a temperature of at least 850oC for at least two seconds. The heat generated by the incineration process has to be put to good use as far as possible. There are strict limit values for incineration plant emissions to air concerning heavy metals and many other toxic emissions.

The Directive requires the installation of measurement systems to monitor the parameters and relevant emission limits. Emissions to air and to water must be measured periodically.

  • Regulation (EC) No. 1774/2002 of the European Parliament and of the Council of 3 October 2002, laying down health rules concerning animal by-products not intended for human consumption.
  • Landfill Directive 99/31/EC

The EU Directive 1999/31/EC on the landfill of waste foresees that "only waste that has been subject to treatment is landfilled." (Article 6 a). In this context, the treatment is defined as "the physical, thermal, chemical or biological processes, including sorting, that change the characteristics of the waste in order to reduce its volume or hazardous nature, facilitate its handling or enhance recovery" (Article 2h). This directive gives a strong push towards any option for recycling and recovery.

The EC Directive 2008/98/EC on waste generally advises to prefer any form of recycling over other types of recovery (e.g. energy recovery) and disposal. It requires that incineration facilities dedicated to the processing of municipal solid waste need to have an energy efficiency equal to or above: 60% for installations in operation and permitted before 1 January 2009, and 65% for installations permitted after 31 December 2008. The efficiency is a cumulated value from electrical and thermal energy resulting from the incineration (this provision of 98/2008 is also known as the R1-formula and is discussed further below)).

  • Packaging and Packaging waste Directive 94/62/EC

The EC Directive 94/62/EC on packaging and packaging waste foresees quotas for the recovery of packaging waste. For plastic packaging waste, a quota of 22,5% by weight has to be recycled or incinerated with energy recovery.

Waste to Energy Incinerators-Main Parts

Furnaces

The prevailing combustion method for municipal solid waste is the so-called 'European Mass Burner', an incineration plant which burns untreated waste on a grate. Typical mass throughput per line is 8 - 25 Mg/h. Grates of all kinds are in use: reciprocating grates, roller grates, reverse acting grates. All these have specific advantages and disadvantages. The reverse acting grate, e.g., has a good vertical mixing and the grate bars are always covered. Hence it can accept rather high calorific waste. However, its incline is high and bigger chunks may roll the grate down without being burnt. Fluidized bed systems build smaller and are mainly found in Japan. In other parts of the world they are more common for biomass combustion and combustion of solid recovered fuels.

Boilers

All modern waste-to-energy plants are equipped with heat recovery systems which are of different design and operate at different steam parameters. A critical component is the super-heater which is typically the section with the highest corrosion attack and hence various solutions to place the super-heater can be found. In grate systems the first part of the boiler is the radiation part followed by a convection section. There are vertical and horizontal boilers in use and in fluidized beds parts of the heat exchange is done in boiler sections submerged in the bed or - in circulating fluidized beds - installed in the ash cycle below the cyclone

Air Pollution Control Systems

Process Stages

In waste incineration the removal of pollutants from the flue gas is one of the most important and most expensive process stages. It can be achieved in many ways. The design of the various configurations found in full scale plants depends not that much upon the clean gas quality - which has to comply with about the same emission standards everywhere - but on investment and/or operation cost, utilization or disposal option of the residues or on available space in the case of upgrading of old facilities.

Today all technologies and all kinds of combinations of abatement options can be found in full scale installations. Each configuration guarantees the compliance with the today's most stringent air emission standards. A selection of the most appropriate gas cleaning strategy depends to a great extent on local conditions. Important factors are administrative regulation (permit for liquid effluents, disposal of solid residues), options, and markets for an eventual recovery and finally the investment and operational costs of the entire system.

In waste incineration plants typically several technology stages are used for the removal of:

  • fly ash,
  • acid gases,
  • specific contaminants like Hg or PCDD/F, and
  • nitrogen oxides.

Following the tendency in modern plants to simplify the gas cleaning procedure some of the stages can be found combined.

Particle Removal

The first step in most APC systems is the fly ash removal which can be done by

  • cyclone,
  • electrostatic precipitator (ESP), or by
  • fabric filter or baghouses.

A cyclone uses inertial impaction for fly ash separation. The gas is entering a cylindrical chamber tangentially at high velocity and is there forced into a cylindrical path. The centripetal force acting on the particles causes them to collide with the walls where they impinge and settle down into the discharge hopper. The gas is extracted through a central tube. A scheme of a cyclone is shown in the left graph of Figure 1. Due to their limited removal efficiency for fine particles cyclones are not often found in modern plants or they serve for pre-deposition of the coarse fly ash.

Figure 1

Figure 1: Scheme of a cyclone (left), an ESP (centre), and a baghouse filter (right)

Due to their simple design, low pressure loss and easy operation ESP are most widely used for fly ash separation in waste incineration but also in other combustion processes like in coal fired power plants. Schemes of the de-dusting principle and of a technical design are shown in the central graph in Figure i. A modern ESP which comprises at least two and often three sectors guarantees dust removal efficiencies of >99 % at particle sizes between 0.01 and >100 μm.

Three field ESP reach clean gas dust levels in the order of 1 mg/m3.

In few installations wet ESP are implemented at the back end for polishing purpose. In these ESP the collecting plates are cleaned with water instead of rapping. The residues from wet ESP are a sludge or suspension and their disposal may cause specific problems.

Even lower emission values than those of ESP can be achieved with fabric or baghouse filters.

In a fabric filter the raw gas passes fabric bags which are supported by metal cages from the outside to the interior. The fly ash stays at the outer surface of the filter bags and is periodically removed by an air pulse blown into the bag from the inner side. This cleaning releases the particles, which fall into the discharge hopper. A scheme of a fabric filter is shown in the right graph of Figure i. Fabric filters guarantee clean gas dust concentrations in the order of 1 mg/m3 and below - if they stay intact.

Chemical Gas Cleaning

The step following a primary fly ash deposition in the air pollution control system is usually the chemical gas cleaning which can be performed in two principal ways:

  • wet-scrubbing and
  • dry scrubbing.

The principle of wet scrubbing is the absorption of gaseous components into a liquid. The efficiency of such absorption process depends first of all on the available surface of the liquid which controls the mass transfer out of the gas into the liquid phase. Different techniques are used to achieve this goal:

  • venturi scrubbers,
  • packed towers,
  • plate and tray towers , and
  • film absorbers.

Wet scrubbing is a common strategy in waste incineration in Central Europe, today in most cases performed as a two-stage installation with an initial acid scrubber followed by a neutral or weakly alkaline one. The acid scrubber is often of the spray or venturi type and reduces the flue gas temperature of 180 - 200 oC down to 63 - 65 oC. In the second stage mainly packed towers are used. Wet systems are operated with (left graph in Figure 2) or, which is the today preferred configuration, without discharge of liquid effluent effluents (right graph in Figure 2).

Figure 2

Figure 2: Schemes of wet scrubbing systems with (left) and without (right) liquid effluents

Such two-stage systems have very high removal efficiencies for the halogen hydrides HF, HCl, and HBr, for mercury, and for SO2. For these components the raw gas concentrations are easily reduced well below the emission standards.

Wet scrubbers were initially operated with discharge of liquid effluents which required a neutralization and an efficient removal of any heavy metal or other toxic contaminant. The standards for water discharge into a sewer are rather stringent and call for high efforts especially in view of Hg and Cd.

The authorities do often prohibit the discharge of waste water. In these cases the scrubbing solutions need to be evaporated which is mainly done in a .spray dryer directly downstream of the boiler (right graph in Figure 2). The solid scrubbing residues are removed from the gas flow in a subsequent - in most cases fabric - filter. An alternative way to evaporate the scrubbing solutions is the external mode by drying in steam heated devices.

Dry and semi-dry scrubbing processes are simple and hence cheap concerning their investment and are in use in many plants all over the world. In most cases the adsorbent is either injected directly into the gas duct or into a spray dryer downstream of the boiler in dry form (dry process) or as a slurry (semi-dry process). The scrubbing products are in most cases removed from the flue gas by a fabric filter. In some installations a separation of the fly ashes prior to the spray dryer may be found. For such purpose in most cases cyclones are installed.

Dry scrubbing can be performed with different reagents, the most common ones are limestone, CaCO3, calcium oxide, CaO, lime, and Ca(OH)2. Today dry processes using CaCO3 have been phased out since they do not guarantee the compliance with the common air emission standards and CaO based processes are for the same reason only implied in cases where the flue gas is humidified prior to the CaO injection. A typical configuration of dry scrubbing is shown in Figure 3.

Figure 3

Figure 3: Scheme of a dry scrubbing system

NOx Abatement

For the abatement of NOx two strategies are followed:

  • the non-catalytic removal (NSCR) by injection of ammonia or another N containing compound into the hot flue gas in the first flue of the boiler at a temperature level around 950 oC, or
  • the selective catalytic reduction (SCR) at a temperature level of 250 to 300 oC, in most cases at the end of the gas cleaning change after reheating of the flue gas.

Advance Thermal Treatment Technologies

Gasification

Gasification is the partial thermal degradation of a substance in the presence of oxygen but with insufficient oxygen to oxidise the fuel completely (i.e. sub-stoichiometric). The general characteristics of gasification of a waste stream are as follows:

  1. A gas such as air, oxygen, or steam is used as a source of oxygen and/or to act as a carrier gas to remove the reaction products from reaction sites;
  2. Moderate temperatures typically above 750 oC;
  3. Products are gas (main combustible components being methane, hydrogen, and carbon monoxide) and a solid residue (consisting of non-combustible material and a small amount of carbon);
  4. The overall process does not convert all of the chemical energy in the fuel into thermal energy but instead leaves some of the chemical energy in the syngas and in the solid residues;
  5. The typical NCV (net calorific value) of the gas from gasification using oxygen is 10 to 15 MJ/Nm3;
  6. The typical NCV of the gas from gasification using air is 4 to 10 MJ/Nm3. For comparison, the NCV for natural gas is about 38 MJ/Nm3.

Gasification offers at least the theoretical potential for innovative use of the product syngas other than immediate combustion to produce heat. Examples of innovative use would be firing of the syngas in gas engines/turbines, the displacement of fossil fuel in large combustion plants or as feedstock for chemicals or liquid fuel production.

Pyrolysis

Pyrolysis is the thermal degradation of a substance in the absence of added oxygen. The general characteristics of pyrolysis of a waste stream are as follows:

  1. No oxygen is present (or almost no oxygen) other than any oxygen present in the fuel;
  2. Low temperatures typically from 300 oC to 800 oC;
  3. Products are syngas (main combustible components being carbon monoxide, hydrogen, methane and some longer chain hydrocarbons including condensable tars, waxes and oils) and a solid residue (consisting of non-combustible material and a significant amount of carbon);
  4. The general lack of oxidation, and lack of an added diluting gas, means that the NCV of syngas from a pyrolysis process is likely to be higher than that from a gasification process (provided substantial quantities of carbon are not left in the solid residues). Typical NCV for the gas produced is 10 to 20 MJ/Nm3;
  5. The overall process generally converts less of the chemical energy into thermal energy than gasification.

Pyrolysis also offers the potential option of more innovative use of the pyrolysis syngas other than immediate combustion to produce heat.

Pyrolysis generally takes place at lower temperatures than for combustion and gasification. The result is less volatilisation of carbon and certain other pollutants such as heavy metals and dioxin precursors into the gaseous stream. Ultimately, the flue gases will need less treatment to meet the emission limits of WID. Any pollutant that is not volatilised will be retained in the pyrolysis residues and need to be dealt with in an environmentally acceptable manner.

The solid residues from some pyrolysis processes could contain up to 40% carbon representing a significant proportion of the energy from the input waste. Recovery of the energy from the char is therefore important for energy efficiency.

The R1-formula

The energy efficiency formula, for simplicity referred to as the R1-formula, determines whether or not a Municipal Solid Waste Incinerator (MSWI) is a recovery operation in respect of R1.

In this context it is important to note, that "recovery" means any operation the principal result of which is waste serving a useful purpose by replacing other materials which would otherwise have been used to fulfil a particular function, or waste being prepared to fulfil that function, in the plant or in the wider economy (Art 3 (15) of Directive 2008/98/EC hereinafter referred to as (WFD).

The non-exhaustive list presented in Annex II of the WFD defines R1 as recovery operations "Use principally as a fuel or other means to generate energy". This includes incineration facilities dedicated to the processing of Municipal Solid Waste (MSW) only where their energy efficiency is equal to or above:

  • 0.60 for installations in operation and permitted in accordance with applicable Community legislation before 1 January 2009,
  • 0.65 for installations permitted after 31 December 2008,
using the following formula:

Figure 3

In which:
Ep means annual energy produced as heat or electricity. It is calculated with energy in the form of electricity being multiplied by 2.6 and heat produced for commercial use multiplied by 1.1 (GJ/year)
Ef means annual energy input to the system from fuel contributing to the production of steam (GJ/year)
Ew means annual energy contained in the treated waste calculated using the net calorific value of the waste (GJ/year)
Ei means annual energy imported excluding Ew and Ef (GJ/year) 0.97 is a factor accounting for energy losses due to bottom ash and radiation

In addition, Annex II of the WFD highlights that this formula shall be applied in accordance with the Reference Document on Best Available Techniques for Waste Incineration (BREF WI).

The formula calculates the energy efficiency of the municipal solid waste incinerator and expresses it as a factor. It calculates the total energy produced by the plant as a proportion of the energy of the fuel (both traditional fuels and waste), being incinerated in the plant. The output of the R1 formula is not the same as power plant efficiency which is typically expressed as a percentage.

Annex II of the WFD clearly restricts the scope of the formula to "Incineration facilities dedicated to the processing of Municipal Solid Waste (MSW)". Hence installations shall correspond to IPPC category 5.2. "Installations for the incineration of municipal waste (household waste and similar commercial, industrial and institutional wastes)". Plants dedicated to co-incineration or incineration plants dedicated to hazardous waste, hospital waste, sewage sludge or industrial waste are thus excluded from the scope of the formula.

The Commission (DG Environment) created an expert working group, consisting of representatives from the Commission and its Joint Research Centre, Member States and stakeholders (industry and NGOs). The aim was to draft a guidance for the application of the formula to make sure it is calculated in a harmonised way across Europe. A consultant (BiPRO) advised the Commission and drafted the different versions of the guidance.

After three meetings of the Working Group the guidance was almost finished and presented to the Member States in the Technical Adaptation Committee (TAC).

The European guidance on the R1 formula will not be endorsed by the Member States in the TAC, and therefore will not be legally binding.

However, as it will be adopted by the Commission's DG Environment after consultation with the other services, including the legal service of the Commission, the Member States and experts, it is expected that Member States will follow the guidance as a helpful tool for a harmonised interpretation of the R1 formula. It is, after all, an expert opinion, which will be taken into consideration by the courts.